This invention involves a process for pulsed-arc welding a metal article in a non-horizontal position. The invention relates to a method of welding together metal articles along a joint using a non-overhanging torch, as shown generally in the FIGURE, that is to say in welding along a vertical joint such as butt welds in a vertical or upright position or in so-called "horizontal-vertical" welding, along a horizontal line to join two vertically disposed articles.
Generally, this technique is satisfactory when cored wire or consumbale flux coated wire called "rutile" wire is usd, that is to say when a wire is used on which the coating has a basis of titanium dioxide. When it is desired simultaneously to obtain a high coating rate, deep penetration, a limitation to the risks of adhesion and inclusions and especially a high resilience which is also displayed at low and very low temperatures, even afte stress relieving treatment, one is necessarily led to use so-called "basis" cored wires. Briefly the flux or coating on a cored wire comprises:
the metal elements: Fe, Mn, Si or a mixture thereof; small quantities of arc stabilizers e.g. the alkali and alkaline earth metals; and scorifiers which will form the slag.
Generally various types of cored wires are distinguished as a function of the composition of the slag which they form depending upon the scorifiers used, i.e.:
(a) scorifiers rich in rutile TiO.sub.2 : "rutile" wires; PA1 (b) scorifiers rich in CaF.sub.2 "fluorspar" basic wires having the following composition: PA1 (a) it does not permit good separation of the slag in order to keep the metal molten; PA1 (b) the erratic arc catches at various points on the molten metal and heats the entire welding pool, making it more fluid; and PA1 (c) the large drops obtained cannot be controlled and transfer metal at various points, as well as liquefying the entire welding pool. PA1 (a) a "pulsed" arc of the constant frequency pulsed kind involving a transfer of molten material with each pulse without setting up a short circuit, PA1 (b) the cored wire electrode being of the basic type.
CaF.sub.2 scorifiers (50%) PA2 other compounds TiO.sub.2, SiO.sub.2, CaO.
The following is an example given in percentages by weight;
Coating:
CaF.sub.2 : 55%
MnO: 12% SiO.sub.2 : 13%
Fe Mn Si: 20%.
These wires are therfore called basic ones because of the basic character of the slag formed and of the scorifiers present. This characteristic is measured by indices such as: ##EQU1## (the numerical values used being the amounts by weight of the substances in the coating.)
Thus the basicity index of the "basic" cored wire described above is four whilst that for a "rutile" type wire is practically O. A "basic" cored wire is one for which the index of basicity is greater than 2. The quantity of coating introduced within the wire varying according to the manufacturer: the composition of the wire (or of the electrode) will be correlated with this (in particular the percentage by weight of CaF.sub.2 in the electrode).
The difference between these different types of cored wires is to be found in the nature of the mechanical properties obtained, principally the notch toughness and tensile characteristics: ultimate tensile strength, yield point, and elongation, after stress relieving treatment. The accepted organizations generally impose, as a function of the type of welded steel:
a minimum notch toughness value, and a tensile strength (in particular a maximum).
By way of example, the following comparative figures are given for notch toughness (charpy V) at -20.degree. C.
______________________________________ Basic Wire Rutile Wire ______________________________________ as welded 13 6 after stress relief 14 4 ______________________________________
It is therefore seen that only one type of basic wire enables high notch toughness values to be obtained and this is the reason why, in certain cases, the use of a "basic" wire is imperative.
Experience has shown that such a basic wire cannot be used in conventional MIG (metal-inert gas) welding technology for out-of-position welding in which the torch does not overhang the joint, as is usually the case in butt welding in a vertical position, as shown in the Figure, or horizontal-vertical welding, because the irregular fusion of such a "basic" wire (in large swirling drops) has the following disadvantages:
The only way to ovecome these disadvantages is to use a coated electrode, which involves a difficult operation if performed manually. The present invention aims at ensuring the result sought by using a wire electrode of basic character and a method of welding which facilitates a high degree of automatic working and therefore achieves a great savings.
According to the present invention, there is used
Experiment has shown that this very specific compromise enables one to obtain in the welding positions considered, a stable welding pool and, as a result of the use of basic cored wires, better values of notch toughness. The pulsed MIG welding technique is directly responsible for this result. The present invention, as well as further objects and advantages thereof, will be understood more clearly and fully from the following description of certain embodiments, with reference to the accompanying drawing.